A tension leg platform (TLP) is a vertically moored floating structure typically used for the offshore production of oil or gas. The platform is permanently moored by means of tethers or tendons connected to the structure of the TLP. A group of tethers is called a tension leg.
Generally the installation process of a TLP is lengthy and extremely expensive. In general, there are two different methods to install a TLP, referred to as pre-installation and co-installation. Conventionally, the pre-installation method initiates by locking the mooring systems, called tendons, into the existing foundation piles. The tendons are held in stable tension using a temporary air can or buoyancy module. The platform is ballasted down onto the tendons and locked into place at the proper draft, then deballasted to the proper tendon tension. The buoyancy cans are then removed, resulting in a stable structure.
The other conventional method of installing a TLP is called co-installation. This method involves assembling the mooring system, also referred to as tendons, prior to TLP installation. All the tendons are hung from the platform and centered over the existing foundation piles. The platform is ballasted down to lock the tendons into to the foundation piles. The platform is then de-ballasted to the proper draft and tendon tension.
The operation of installing a TLP, whether pre-installation or co-installation, is very time consuming and costly. This is especially true for the process of ballasting and de-ballasting the hull. Hull ballasting requires the movement of millions of gallons of seawater. This process typically takes up to 24 to 48 hours to complete. A need exists for a technique to reduce ballasting time while reducing unnecessary and costly installation equipment for both types of TLP installation methods.